Showing papers on "Power system simulation published in 2002"

General model for representing variable speed wind turbines in power system dynamics simulations

Abstract: A tendency to erect ever more wind turbines can be observed in order to reduce the environmental consequences of electric power generation. As a result of this, in the near future, wind turbines may start to influence the behavior of electric power systems by interacting with conventional generation and loads. Therefore, wind turbine models that can be integrated into power system simulation software are needed. In this contribution, a model that can be used to represent all types of variable speed wind turbines in power system dynamics simulations is presented. First, the modeling approach is commented upon and models of the subsystems of which a variable speed wind turbine consists are discussed. Then, some results obtained after incorporation of the model in PSS/E, a widely used power system dynamics simulation software package, are presented and compared with measurements.

Optimal des'ign of Power System Stabilizers Using Particle Swarm Opt'imization

Abstract: In this paper, a novel evolutionary algorithm-based approach to optimal design of multimachine power system stabilizers (PSSs) is proposed. The proposed approach employs the particle swarm optimization (PSO) technique to search for optimal settings of PSS parameters. Two elgenvalue-based objective functions to enhance system damping of electromechanical modes are considered. The robustness of the proposed approach to the initial guess is demonstrated. The performance of the proposed PSO-based PSS (PSOPSS) under different disturbances, loading conditions, and system configurations is tested and examined for different multimachine power systems. Eigenvalue analysis and nonlinear simulation results show the effectiveness of the proposed PSOPSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations. In addition, the potential and superiority of the proposed approach over the conventional approaches are demonstrated.

Oligopolistic competition in power networks: a conjectured supply function approach

Abstract: Conjectured supply function (CSF) models of competition among power generators on a linearized DC network are presented. As a detailed survey of the power market modeling literature shows, CSF models differ from previous approaches in that they represent each generation company's (GenCo) conjectures regarding how rival firms will adjust sales in response to price changes. The CSF approach is a more realistic and flexible framework for modeling imperfect competition than other models for three reasons. First, the models include as a special case the Cournot conjecture that rivals will not change production if prices change; thus, the CSF framework is more general. Second, Cournot models cannot be used when price elasticity of demand is zero, but the proposed models can. Third, unlike supply function equilibrium models, CSF equilibria can be calculated for large transmission networks. Existence and uniqueness properties for prices and profits are reported. An application shows how transmission limits and strategic interactions affect equilibrium prices under forced divestment of generation.

A multi-agent approach to power system restoration

Abstract: This paper proposes a multi-agent approach to power system restoration. The proposed system consists of a number of bus agents (BAGS) and a single facilitator agent (FAG). BAG is developed to decide a suboptimal target configuration after a fault occurrence by interacting with other BAGS based on only locally available information, while FAG is to act as a manager in the decision process. The interaction of several simple agents leads to a dynamic system, allowing efficient approximation of a solution. Simulation results have demonstrated that this method is able to reach suboptimal target configurations, which are favorably compared with those obtained by a mathematical programming approach.

Modeling of wind turbines for power system studies

Abstract: In this paper, the modeling of wind turbines for power system studies is investigated. Complexities of various parts of a wind turbine model, such as aerodynamic conversion, drive train, and generator representation, are analyzed. The results are verified by field measurements made on a stall-regulated fixed-speed wind turbine. The modeling focuses on deriving a representation that is suitable for use in grid simulation programs.

Short-Term Generation Asset Valuation: A Real Options Approach

Abstract: This paper discusses using real options to value power plants with unit commitment constraints over a short-term period. We formulate the problem as a multistage stochastic problem and propose a solution procedure that integrates forward-moving Monte Carlo simulation with backward-moving dynamic programming. We assume that the power plant operator maximizes expected profit by deciding in each hour whether or not to run the unit, that a certain lead time for commitment and decommitment decisions is necessary to start up and shut down a unit, and that these commitment decisions, once made, are subject to physical constraints such as minimum uptime and downtime. We also account for the costs associated with starting up and shutting down a unit. Last, we assume that there are hourly markets for both electricity and the fuel used by the generator and that their prices follow Ito processes. Using numerical simulation, we show that failure to consider physical constraints may significantly overvalue a power plant.

Application studies of superconducting fault current limiters in electric power systems

Abstract: In power systems, superconducting fault current limiters (SFCLs) can limit the prospective short-circuit currents to lower levels, so that the underrated switchgear can be operated safely. This paper presents a detailed theoretical analysis of improving power system stability by using SFCLs. Electromagnetic Transient Program (EMTP) simulation results based on a model system also show that SFCLs are effective for enhancing the transient stability of electric power systems by restraining the generator rotors from accelerating after faults and improving power quality. This paper outlines the basic application guidelines for using superconducting fault current limiters in different voltage-level power systems. In order to insure the safe and proper usage of SFCLs, some future considerations on the interaction between SFCLs and power systems are presented as well.

Incidence on power system dynamics of high penetration of fixed speed and doubly fed wind energy systems: study of the Spanish case

Abstract: In this paper, a preliminary analysis of the impact of high wind power penetration in the planning and operation of the Spanish power system is presented. The problems studied in the paper are those related to the stability of the power system. This key subject could be deeply influenced by the installation of up to 15000 MW of wind power generation as it has been planned for the next six years. The analysis presented here is based on the results of dynamic simulations. Dynamic models of the induction generator (squirrel cage and doubly fed) and models of the wind farms have been developed to make possible the simulations. From the simulation results some conclusions and recommendations have been extracted, which would contribute to the appropriate integration of the new wind generation foreseen for the Spanish power system.

A unit commitment problem by using genetic algorithm based on unit characteristic classification

Abstract: This paper presents new approach for thermal unit commitment problem. Unit commitment (UC) problem plays a major role in power systems since the improvement of commitment schedules results in the reduction of operating cost. However, the unit commitment problem is one of the most difficult optimization problems in power system, because they have many constraints. Further, these constraints vary with each unit. To handle these constraints, some cording methods have been proposed. However, these methods require computation time. To overcome these problems, a new genetic operator based on unit characteristic classification and intelligent techniques generating initial populations are introduced. The proposed algorithm was tested on a reported UC problem. From simulation results, satisfactory solutions are obtained in comparison with previously reported results. Numerical results for system of up to 100 units are compared to previously reported results.

Teaching nonlinear modeling, simulation, and control of electronic power converters using MATLAB/SIMULINK

Abstract: This paper describes an efficient method to teach analysis and simulation of power electronic converters to undergraduate students, using system level nonlinear state-space models. System-level modeling of power electronic converters reproduces only the ideal switching behavior of the semiconductors and is a useful concept for the numerical simulation of power converters, since simulations present no convergence problems and require little computational time. Switched state-space models, programmed in the MATLAB/SIMULINK software package, can be advantageously used to simulate power converters at the system level and also to design and study their controllers. Switched state-space nonlinear models should be obtained using a theoretical framework suitable for the enhanced control of variable structure power systems. Since the method is inherently nonlinear, no approximated linear models are needed; and since state-space models are used, modern control techniques (sliding mode, neural networks, fuzzy logic) for power converters can easily be used. This paper summarizes the proposed methodology and gives some examples.

Optimal design of power system stabilizers using evolutionary programming

Abstract: The optimal design of power system stabilizers (PSSs) using evolutionary programming (EP) optimization technique is presented in this paper. The proposed approach employs EP to search for optimal settings of PSS parameters that shift the system eigenvalues associated with the electromechanical modes to the left in the s-plane. Incorporation of EP algorithm in the design of PSSs significantly reduces the computational burden. The performance of the proposed PSSs under different disturbances, loading conditions, and system configurations is investigated for a multimachine power system. The eigenvalue analysis and the nonlinear simulation results show the effectiveness and robustness of the proposed PSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations.

A hybrid LR-EP for solving new profit-based UC problem under competitive environment

Abstract: With the opening of the power industry to competition, the power system structure is changing. According to these changes, power system operation, planning, and control need modifications. In the past, utilities had to produce power to satisfy their customers with objective to minimize costs and all demand/reserve were met. However, it is not necessary in a restructured system. Under new structure, generation companies (GENCOs) schedule their generators with objective to maximize their own profit without regard for system social benefit. Power and reserve prices become important factors in decision process. This paper proposes a new tool, profit-based unit commitment (UC) considering power and reserve generation. The proposed method helps GENCO to make a decision, how much power and reserve should be sold in markets, and how to schedule generators in order to receive the maximum profit. A hybrid method between Lagrange relaxation (LR) and evolutionary programming (EP) is used for solving this problem. Simulations are carried out to show the performance of the proposed methodology.

Adaptation in load shedding under vulnerable operating conditions

Abstract: The proposed approach to avoiding catastrophic failures in interconnected power systems uses a defeusive system based on multiagent system technologies. Because of their dynamic environments, these agents need to automatically adjust their decision criteria. The method of reinforcement learning with temporal differences can provide a suitable basis for the adaptation. An appropriate convergence criterion is derived and an application of the method to load shedding is demonstrated. A dynamic simulation involving a 179-bus power system is used to validate the method.

Simulation of interaction between wind farm and power system

Abstract: A dynamic model of the wind farm Hagesholm has been implemented in the dedicated power system simulation program DIgSILENT. The wind farm consists of six 2MW NM2000/72 wind turbines from NEG-Micon. The model has been verified using simultaneous power quality measurements on the 10 kV terminals of a single wind turbine and power performance measurements on two wind turbines. The verification shows a generally good agreement between simulations and measurements, although the simulations at higher wind speeds seem to underestimate the power and voltage fluctuations. A way to improve the simulation at higher wind speeds is suggested. This report has passed the internal review performed by Peter Hauge Madsen Frede Blaabjerg ISBN 87-550-2912-4 ISBN 87-550-2913-2 (Internet) ISSN 0106-2840 Print: Pitney Bowes Management Services Denmark A/S, 2001 Riso-R-1281(EN) 3

A two-stage planning model for power scheduling in a hydro-thermal system under uncertainty

Abstract: A two-stage stochastic programming model for the short- or mid-term cost-optimal electric power production planning is developed. We consider the power generation in a hydro-thermal generation system under uncertainty in demand (or load) and prices for fuel and delivery contracts. The model involves a large number of mixed-integer (stochastic) decision variables and constraints linking time periods and operating power units. A stochastic Lagrangian relaxation scheme is designed by assigning (stochastic) multipliers to all constraints that couple power units. It is assumed that the stochastic load and price processes are given (or approximated) by a finite number of realizations (scenarios). Solving the dual by a bundle subgradient method leads to a successive decomposition into stochastic single unit subproblems. The stochastic thermal and hydro subproblems are solved by a stochastic dynamic programming technique and by a specific descent algorithm, respectively. A Lagrangian heuristics that provides approximate solutions for the primal problem is developed. Numerical results are presented for realistic data from a German power utility and for numbers of scenarios ranging from 5 to 100 and a time horizon of 168 hours. The sizes of the corresponding optimization problems go up to 400.000 binary and 650.000 continuous variables, and more than 1.300.000 constraints.

Dynamic modelling of wind farm grid interaction

Abstract: This paper describes a dynamic model of a wind farm and its nearest utility grid. It is intended to use this model in studies addressing the dynamic interaction between a wind farm and a power system, both during normal operation of the wind farm and during transient grid fault events. The model comprises the substation where the wind farm is connected, the internal power collection system of the wind farm, the electrical, mechanical and aerodynamic models for the wind turbines, and a wind model. The integrated model is built to enable the assessment of power quality and control strategies. It is implemented in the commercial dedicated power system simulation tool DIgSILENT.

PAT: a power analysis toolbox for MATLAB/Simulink

Abstract: A power system simulation environment in MATLAB/Simulink is presented in this paper. The developed power analysis toolbox (PAT) is a very flexible and modular tool for load flow, transient, and small-signal analysis of electric power systems. Standard power system component models and a wide range of flexible AC transmission systems (FACTS) devices are included. Its data structure and block library have been tested to confirm its applicability to small-to-medium-sized power systems. Its advantages over an existing commercial package are given.

Modeling of UPFC operation under unbalanced conditions with dynamic phasors

Abstract: The paper describes an analytical large-signal model for unbalanced operation of the unified power flow controller (UPFC). This nonlinear, time-invariant model is expressed in terms of dynamic symmetric components, and it is validated on a benchmark power system example taken from the literature. The model is evaluated via simulations in unbalanced operation and during unbalanced (one phase to ground) faults. In both cases, it achieves a very good accuracy, in addition to a reduction in simulation time when compared with detailed time-domain models.

Power management in a hydro-thermal system under uncertainty by Lagrangian relaxation

Abstract: We present a dynamic multistage stochastic programming model for the cost-optimal generation of electric power in a hydro-thermal system under uncertainty in load, inflow to reservoirs and prices for fuel and delivery contracts. The stochastic load process is approximated by a scenario tree obtained by adapting a SARIMA model to historical data, using empirical means and variances of simulated scenarios to construct an initial tree, and reducing it by a scenario deletion procedure based on a suitable probability distance. Our model involves many mixed-integer variables and individual power unit constraints, but relatively few coupling constraints. Hence we employ stochastic Lagrangian relaxation that assigns stochastic multipliers to the coupling constraints. Solving the Lagrangian dual by a proximal bundle method leads to successive decomposition into single thermal and hydro unit subproblems that are solved by dynamic programming and a specialized descent algorithm, respectively. The optimal stochastic multipliers are used in Lagrangian heuristics to construct approximately optimal first stage decisions. Numerical results are presented for realistic data from a German power utility, with a time horizon of one week and scenario numbers ranging from 5 to 100. The corresponding optimization problems have up to 200,000 binary and 350,000 continuous variables, and more than 500,000 constraints.

Real time network simulation with PC-cluster

Abstract: This paper presents a new architecture layout for a real-time power system simulator based on a distributed cluster of IBM PC-compatible desktop computers. A real-time network simulator based on a PC cluster can successfully cope with the size requirements of growing power systems and the computational demands of fast transient studies. A powerful product has been developed using off-the-shelf Pentium II 400-MHz workstations with a commercial real-time operating system, standard input/output (I/O) interfaces, and a multimachine networking scheme. Models based on the standard tool for power systems transients simulations, the Electromagnetic Transients Programs (EMTP) program, optimized for real-time performance ensure accurate simulation results.

Modeling and control of a multi-agent system using mixed integer linear programming

Abstract: The RoboFlag competition was proposed by the second author as a means to study cooperative control of multi-vehicle systems. Here we study a simplified version of the competition that we model as a hybrid system. We use an optimization approach to synthesize control policies by solving mixed integer linear programs.

Unit commitment using the ant colony search algorithm

Abstract: The paper presents an ant colony search algorithm (ACSA)-based approach to solve the unit commitment (UC) problem. This ACSA algorithm is a relatively new meta-heuristic for solving hard combinatorial optimization problems. It is a population-based approach that uses exploitation of positive feedback, distributed computation as well as a constructive greedy heuristic. Positive feedback is for fast discovery of good solutions, distributed computation avoids early convergence, and the greedy heuristic helps find adequate solutions in the early stages of the search process. The ACSA was inspired from natural behavior of the ant colonies on how they find the food source and bring them back to their nest by building the unique trail formation. The UC problem solved using the proposed approach is subject to real power balance, real power operating limits of generating units, spinning reserve, start up cost, and minimum up and down time constraints. The proposed approach determines the search space of multi-stage scheduling followed by considering the unit transition related constraints during the process of state transition. The paper describes the proposed approach and presents test results on a 10-unit test system that demonstrates its effectiveness in solving the UC problem.

Power system considerations for undersea observatories

Abstract: Power systems for undersea observatories combine ideas from terrestrial power systems and switching power supplies with experience from undersea cable systems. Basic system tradeoffs for various design decisions are explored in this paper. First, design questions including whether the power delivery should be alternating or direct current and a parallel or series network are examined. This introduces the question of maximum power delivery capability, which is explored in depth. A separate issue, the negative incremental resistance presented to the delivery system by the use of constant-voltage converters, is examined, and the resulting dynamics explored by simulation.

Modelling and simulation of a single-phase AC-AC matrix converter using SPWM

Abstract: This paper presents work carried out in developing computer simulation models using the Power System Block Set (PSB) within the MATLab/Simulink (MLS) environment. Its powerful filter design tools, signal processing capabilities are used to illustrate the convenience of modelling and simulation. The SPMC as a direct frequency changer were used in this work with the output being synthesized using the well-known SPWM technique. A comparison was made with SPICE and has shown that results in PSB were in good agreement from simulations carried out.

Genetic algorithm based inter-area oscillation damping controller design using MATLAB

Abstract: This paper presents a GA based optimization scheme for simultaneous coordination of multiple power system damping controllers. Both, local and remote, measurements are considered as input signals to the damping controllers. The proposed algorithm is applied to tuning of single and multiple power system stabilizers as well as tuning of a static VAr compensator. Controller design is tested on the small and mid-sized power systems to prove its effectiveness. All simulations are carried out using the MATLAB based package for nonlinear simulations of power systems, Power Analysis Toolbox (PAT), developed at West Virginia University's Advanced Power Engineering Research Center. Controllers are designed using MATLAB Control System Toolbox and optimized using GAOT toolbox.

Modeling combined-cycle power plant for simulation of frequency excursions

Abstract: The maximum continuous power output of a combined-cycle power plant depends on the system frequency and the ambient temperature. The temperature control of a gas turbine limits the exhaust temperature by reducing the fuel flow as the airflow decreases with the shaft speed. In this paper, a simple model of a combined-cycle power plant is derived from a detailed design model for an example plant. The model is suitable for long-term simulation of power system dynamic performance involving abnormal frequency conditions.

MATLAB/Simulink-Based Transient Stability Analysis of a Multimachine Power System:

Abstract: Simulink is advanced software by MathWorks Inc., which is increasingly being used as a basic building block in many areas of research. As such, it also holds great potential in the area of power system simulation. In this paper, we have taken a multi-machine power system example to demonstrate the features and scope of a Simulink-based model for transient stability analysis. A self-sufficient model has been given with full details, which can work as a basic structure for an advanced and detailed study.

Modeling and simulation of grid connected wind electric generating system

Abstract: The effects of variation in grid voltage and frequency on the performance of the grid connected wind electric generating system has been studied for various wind velocities The induction generator, wind turbine and other network components are modeled using MATLAB/SIMULINK The model has been made realistic by considering the nonlinear variation of R/sub m/ and X/sub m/ of the induction generator A simple simulation procedure is developed to predict the system performance and the results are presented The dynamic VAr compensation by using TSC is also studied and the best location for the compensating capacitor is suggested

A practical direct method for determining dynamic security regions of electrical power systems

Abstract: The dynamic security region (DSR) of an electrical power system has been accepted more and more for providing plenty of security information and good prospects in online application. This paper presents a direct method for determining the practical DSR (PDSR) via the analysis of transient energy. The key feature of such a method is the parallel character of the boundaries of transient stability region at the exit points under different critical power injections. Based on this parallel character, a hyper-plane expression of the boundary of the PDSR and corresponding algorithm are proposed in the paper. The method developed is simple and fast. It has been evaluated on the New England Test System, which agrees closely with the results of simulations.

Simulation of FACTS controllers using the MATLAB Power System Blockset and Hypersim real-time simulator

Abstract: This presentation explains the simulation tools and the solution methods used in the Hydro-Quebec Power System Simulation laboratory for the design and real-time testing of FACTS controllers. Hypersim is the ultimate simulation method because it allows real-time testing of FACTS controllers or fast off-line simulation on a multiprocessor system. Also, the three simulation methods available in PSB are efficient techniques for design and analysis of complex control systems found in FACTS and custom power controllers.